Separate Compilation. Comparison. Single Source File Programs Programs where all the code is contained within 1 file.

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1 Separate 1 Comparison 2 Table of Contents Sgle Source File Programs Programs where all code is contaed with 1 file. Comparison Large s results problems. Files Module Structure Security Issues Global Concerns Header Inclusion Problem Portability Disadvantages Very long compile time Errors requires recompilation of entire Difficult to edit Multi-File Programs Module Scope Code for a is stored several source files. Design Problem Code Redesign Redesign Solution Example: Addresses Example: C++ Code #1 Example: C++ Code #2 Example: C++ Code #3 Example: C++ Code #4 Advantages Decreases reompile time for errors. Modification of code one file NOT require compilation of or files, (exception: if function terfaces have changed). Programs can be broken to smaller, simpler subsystems. Separate compilation helps support d methods and modular decomposition for developg large systems. Allows languages to be used conjunction with or mg languages. Eases testg large systems. Allows aess to system functions, code libraries and packages. Facilitates code reusability.

2 Files 3 Module Structure 4 Separate Steps Step 1 source files compiled to object files Step 2 objects files lked to form executable image a.h a. a. a. Object files conta mache code but not executable form. Object files conta references (calls) to external functions that must be resolved. Lker s (UNIX lker is ln), are commonly voked by (C/C++) compilers: C++ Module Components Two Files: a.h Interface File: (header file.h) contas public declarations of all articles that are aessible (visible) and usable by external modules that clude terface file. Articles consist of constants, typedefs, and function prototypes (only parameter types need to be specified, parameter names cluded are ignored by compiler). c. c. d. d. c.h c. c.o exe d.o d. d.h a.cpp Implementation File: (code file.c or.cpp) contas private declarations and defitions of all articles that are aessible (visible) and NOT usable by external modules that clude terface file. A change one module (requires only 1 recompile: a. a. Followed by relkg: c.o c.o d.o d.o -o -o exe exe b. b. b. b.h Changg header files requires recompilg all files cludg headers. c.o c.o d.o d.o -o -o exe exe vokes C/C++ compiler. equivalent to.cpp.o equivalent to.obj The full declarations of function protypes given header file are specified. Articles declared implementation file that are NOT declared terface file are considered local/ternal to module and can only be aessed by module s code NOT by external code.

3 Security Issues Traditional C Function Declarations Parameter type lists cannot be cluded Fn declarations t fn( ); 5 Security Issues (contued) Traditional C Function Invocation Declarations Function calls prior to fn declarations results default declarations. Example: 6 ANSI C compilers will aept traditional C Fn declarations. Compiler NOT know types of parameters. Compiler cannot perform type checkg on arguments. Compiler cannot perform coercion/conversion/promotg between parameters & arguments. longt = fn(longt); above call will yield correct results Mixg Traditional C & C++ Function Declarations Prototypes are required C++ In defg functions and ir prototypes, usg void parameter types lists is optional: void fn(); «=» void fn( void ); void is NOT a keyword traditional C t fn(); The above declaration specifies that fn aepts an unknown number of arguments. fn(x); /* encountered before fn declaration */ Assumed default declaration: t fn(); Parameter list attributes are unknown. No type checkg or coercion/conversion can be performed. Traditional C Function Defitions & Invocation Traditional C fn defition/declaration prior to vocation: t fn(x); long x; } Traditional C compilers still treat parameter list attributes as unknown. Programmer has responsibility for ensurg that correct number and type of arguments are passed. C++ Function Prototypes Compiler performs type checkg of parameters & arguments.

4 Global Concerns Declarations & Defitions Declarations give only attributes of identifiers (type). Defitions give attributes of identifiers and reserves storage. Identifiers can only be defed once a, but may be declared multiple times. Defitions should NOT be placed header files. External Defitions Defitions that our outside all functions a file. Scope extends to end of file. Cannot be aessed outside of file, unless declared as an extern identifier separately compiled files. extern t x; extern void fn(long); Array sizes must be given defitions but are optional declarations. Extern declarations are NOT defitions (no storage is reserved, no itialization can be performed). Global (separate compilation) Variables extern declarations allow for common storage across compilation units. extern declarations are to avoided at all costs due to same problems herent ir use sgle file s. 7 Header Inclusion Problem Problem Statement Separate files may use same header file. Assume a mer has stored system wide constants : const.h Assume const.h is cluded modulea header file: modulea.h Assume moduleb cludes modulea.h and const.h. const.h header defitions would be duplicated moduleb. after preprocessg Solution: Conditional Preprocessor directives: #if #ifdef #ifndef #undef Usage: const.h #ifndef #defe type defitions, constants, etc... CONST_H CONST_H CONST_H CONST_H is is a a preprocessor preprocessor identifier identifier not not a a C/C++ C/C++ identifier identifier Inclusion of const.h structs preprocessor to check if CONST_H has been previously defed durg preprocessg. If it has not n it is defed and const.h declarations are copied to source orwise no clusion ours. 8

5 Portability defed Preprocessor Directive defed < identifier > Evaluates to true if identifer has been previously defed preprocessg. Platform Specific #defe WIN95 or #defe WINNT #if defed(win95 ) Preprocessor Preprocessor // WIN95 specific code directives directives or or #elif defed(winnt) than than those those covered covered // WINNT specific code here here are are available. available. #else Debuggg Can be utilized to compile or skip diagnostic output statements #defe DEBUG 1 Two Methods: #if DEBUG cout << Debug: << strg1 << endl; #defe DEBUG #ifdef DEBUG cout << Debug: << strg1 << endl; 9 Module Scope Lifetime Variables declared above all functions a source file (filescoped) and side of ma() exist throughout execution (life) of sce ma() drives all or routes. All or variables declared side of functions exist only for lifetime (execution) of function (automatic) excludg static (and extern). Restricted Aess Given diagram at right: The ma only needs to call routes unit A, and not require any aess to routes, consts, or or elements unit B. Unit A needs only to call routes unit B. //ma.cpp //ma.cpp ma.h ma.h const.h const.h unita.h unita.h void ma() void ma() } } unita ma prog No direct or direct usage unitb // // unita.cpp unita.cpp const.h const.h unita.h unita.h unitb.h unitb.h // // unitb.cpp unitb.cpp const.h const.h unitb.h unitb.h 10

6 Design Problem Restricted Aess Problem: Special graphical /debug routes need to be executed at particular times durg system execution. Trace flag is not needed for unita or unitb. Complicates terfaces and exposes to possible or aidental misuse. On() Insert() unita() ma() unitb() Off() Delete() showinsert() sert() delete() showdelete() Solution 1: Make Trace global. Uncomplicates terfaces but not solve scope problem. Solution 2: Hide private declarations of a separately compiled module, limit aess to module functions. 11 Code Redesign r.h r.cpp #ifndef TRACER_H #ifndef TRACER_H #defe TRACER_H #defe TRACER_H void ittrace(void) ; void ittrace(void) ; void On(void) ; void On(void) ; void Off(void) ; void Off(void) ; bool Active(void); bool Active(void); r.h r.h bool bool ; ; void void ittrace(void) ittrace(void) = false; } = false; } void On(void) void On(void) = true; } = true; } void Off(void) void Off(void) = false; } = false; } bool Active() bool Active() return ; } return ; } 12 Localized Localized global global variable variable can can aessed aessed and and changed changed any any function function r., r., but but NOT NOT any any code code external external to to r. r.

7 Redesign Solution 13 Example: Addresses 14 Tradeoff Interface simplification achieved at crease of number of system modules. Reference adapted from: Programmg and Problem Solvg with C++, N. Dale, C. Weems & M. Headgton, D.C. Heath, 1996, Ma ma() Init() On() unita() unitb() Off() somefile entry item list length address Book length friend- File Insert() Delete() Active() Active() Active() showinsert() sert() delete() showdelete() Open For Output Get Name entry Get Entry entry item length Get Phone Number Insert list SearchOrd dex found Write Entries Units friends.cpp GetEntry.cpp sert.cpp

8 Example: C++ Code #1 15 Example: C++ Code #2 16 globals.h * // globals.h header file * #ifndef GLOBALS_H #defe GLOBALS_H <iostream.h> <iomanip.h> <fstream.h> <ctype.h> const t MAX_FRIENDS = 150; typedef char Strg8[9]; typedef char Strg15[16]; // For setw() // For file I/O // For toupper() // Max number of friends // 8 characters plus '\0' // 15 characters plus '\0' struct EntryType Strg15 firstname; Strg15 lastname; t areacode; // Range Strg8 phonenumber; t month; // Range t day; // Range t year; // Range }; void OpenForOutput( ofstream& ); void WriteEntries( const EntryType[], t, ofstream& ); friends.cpp // This creates an address book by readg // first names, last names, phone numbers, and birth // dates from standard put and writg an alphabetical // listg to an output file "globals.h" "GetEntry.h" "sert.h" // global constants & types // address book buildg // sert sort of address book t ma() EntryType addressbook[max_friends]; // friends' recs t length = 0; // Number entries addressbook EntryType entry; // Current rec beg read char response; // Response char ofstream friendfile; // Output file entries OpenForOutput(friendFile); if (!friendfile ) return 1; // globals.h globals.h NOT NOT correctly correctly chart chart design. design.

9 Example: C++ Code #3 17 Example: C++ Code #4 18 GetEntry.h sert.h // GetEntry.h header file // sert.h header file #ifndef GetEntry_H #defe GetEntry_H #ifndef INSERT_H #defe INSERT_H Why Why sert.h sert.h correctly correctly design design of of chart? chart? "globals.h" void GetEntry( EntryType& ); void GetName( EntryType& ); void GetPhoneNumber( EntryType& ); GetEntry.cpp // For global constants & types // GetEntry.cpp file "GetEntry.h" Why Why GetEntry.h GetEntry.h correctly correctly design design of of chart? chart? // For header file <strg.h> "globals.h" sert.cpp // For strcmp() // For global constants & types void Insert( EntryType[], t&, EntryType ); void SearchOrd( EntryType[], EntryType, t, t&, bool& ); // sert.cpp file "sert.h" // For header file void GetEntry( /* out */ EntryType& entry ) GetName(entry); GetPhoneNumber(entry); cout << "Enter birth date as 3 tegers, separated by" << " spaces: MM DD YYYY" << endl; c >> entry.month >> entry.day >> entry.year; // void Insert( /*out*/ EntryType list[], // Changed List /*out*/ t& length, // List Length /**/ EntryType item ) // Insert Item // Inserts item to its proper place sorted list //

Comparison. Separate Compilation

Comparison. Separate Compilation Separate Slides 1. Table of Contents 2. Comparison 3. Files 4. Module Structure 5. Security Issues 6. Security Issues (cont) 7. Global Concerns 8. Header Inusion Problem 9. Portability 10. Module Scope